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Methods of Part Ejection
Did you know?
Common ejection methods include ejector pins, ejector sleeves, ejector blades and stripper plates. Designers should be aware of these methods which serve to push the plastic part out of the mold after it has solidified. Knowing this, they can accommodate such devices in the part design and be aware of the effect of their presence on the surface of the part. Ejectors also serve to push out the runner system and break free a runner system from the part at a sub gate. Ejectors can also provide a means for venting gases out of a cavity, thereby improving the cosmetic appearance of a part.
Ejector pins and ejector blades and to a lesser extent the stripper plate and ejector sleeves, all leave a witness mark on the finished part. The ejector pin and blade will either leave an impression or a protrusion where the pin or blade is located on the part.
The number and size of the ejectors used is dependant on the size and shape of the part. It is important to provide a balanced pressure on the part so that the part is not deformed during ejection.
The common methods of part ejection are discussed below;
Ejector Pins - round pins of varying diameters, placed in strategic locations on the core side of the mold (see figure 1).
Figure 1. Typical Mold with Ejector Pins
Ejector Sleeves – an ejector sleeve is basically an ejector pin with a hole through the center. The hole is used for a core pin to form a portion of the desired part. The actuation of an ejection sleeve is like an ejector pin (see figure 2). They are typically used for pushing off cylindrical parts like bosses or long thin walled tubular parts.
Figure 2. Ejector Sleeve
Ejector Blades – an ejector blade is essentially an ejector pin with a flattened tip – instead of being circular in cross section, it would be rectangular. Blade ejectors are most commonly used with ribbed parts and under thin walls where ejector pins would prove to be too small and weak.
Stripper Plates – are used to strip the part off the core steel. The stripper plate is actuated via stripper bolts from the cavity side of the mold or by the ejector mechanism (see figure 3).
Figure 3. A Mold with Stripper Plate Actuated from the Ejector Plate |
